The invention relates generally to mine ventilation control, and specifically to a method and apparatus for supporting ventilation curtains in mine entries.
In mining coal underground, the room and pillar method of mining is often used. As shown in FIG. 1, mine sections are usually constructed with multiple parallel entries 10, extending from the opening 12 of the section to the face 14 of the mine where the coal or other material is being cut. As the coal is mined, dust and gases are liberated at the face 14, which, if left to accumulate, could build up to form explosive or otherwise harmful concentrations. Accordingly, ventilation systems are used to remove escaping gases and/or dust. Typically, at least one of the entries 10 serves as an intake air course to provide ventilation to the face 14, while other entries provide return air courses and neutral entries for belt and trolley haulage to convey the mined material from the face of the mine. As the face of the mine advances, transverse crosscuts 16 are placed approximately every 80' (25 m) (this distance may vary from 40' to 90' (13 m to 29 m), or over a greater range, depending on applicable regulations and exceptions) to provide communication between the entries 10 and thus ventilation across the entire mine face 14. The axially-extending entries 10 and spaced transverse crosscuts 16 thus define pillars 18 extending along the entire mine section.
To assure delivery of fresh air to the mine face 14 at an adequate velocity, a pressure differential must be established between the intake and return air courses (typically by a mine fan), as well as the haulage courses. Therefore, the crosscuts 16 must be blocked by placing stoppings 22 across each crosscut from pillar to pillar and floor to ceiling. Most of the stoppings 22 are of permanent construction (such as cement and cinder block), while, be regulation, the stoppings in the last two crosscuts closest to the mine face (as at 23) may be temporary stoppings of less durable construction, typically of sheets of fire-resistant, gas impervious material.
To ensure that the ventilating air does not return along intermediate entries 10, the entries (other than the intake and return air courses) are blocked by check curtains 24 between the pillars 18 closest to the face 14. The check curtains have flaps that open to permit passage of workers and equipment then close to maintain an air seal. Finally, to provide adequate flow directly across the face 14, line curtains 26 are placed to extend from the face to the pillars 18 closest to the face. Thus, ventilating air A can flow down the intake course, along and around the end of line curtains 26, across the face 14, and out along the return course.
A variety of techniques are known for constructing these ventilation structures. One portable stopping construction is disclosed in U.S. Pat. No. 3,863,554 to Boyd. The portable stoppings 38 are formed of flexible sheet 40 supported on a frame structure 41 between the roof, floor, and side ribs of the crosscuts 35. The frame 41 is formed of telescoping vertical support rods 42, horizontal support rods 43, and diagonal support rods 44, while the perimeter of the frame 41 is defined by metal straps 45. The edges 46 of the sheet 40 are folded over the strap 45 so that several layers of the sheet are trapped between the strap and the adjacent mine surface S. When the support rods 42, 43, and 44 are extended by jacks, the straps press the layers against the mine surface to form a seal. Spikes 48 can also be used to penetrate the straps, sheet material, and mine surface to retain the straps and sheet material to the mine surface. The system of support rods and straps is complex and cumbersome, and the spikes damage the sheet material, limiting the number of times the material can be reused.
Several techniques are known for suspending sheet materials for use as stoppings, check curtains, and line curtains. U.S. Pat. No. 1,778,979 to Lockhart discloses a curtain formed of fabric strips 31 with a reinforcing member 32 (such as a wire) extending along the top end the strip. Holes are drilled in the roof of the mine and wooden plugs driven into the holes. Staples are then driven into the wooden plugs, the staples straddling the reinforcing wire 32 and holding the top of the fabric strips against the mine roof. In U.S. Pat. No. 2,947,239 to Burgess, the top of the curtain material is provided with grommets that are mounted on hooks secured to the mine's supporting timbers. These techniques rely on the presence of supporting timbers and the placement of hooks or on the cumbersome and time-consuming process of drilling holes and placing wooden plugs, and require specialized curtains.
U.S. Pat. No. 3,118,363 to Burgess discloses a spring-loaded, two-piece supporting assembly 12 fitted with spikes 30 and 36 at the top and bottom to engage the roof and floor of the mine, respectively. The supporting assembly is also fitted with a hook 48 that engages grommets fitted to the top edge of the sheet 10. A series of supporting assemblies are fitted vertically between the roof and floor of the mine, and the sheet 10 hung from the hooks 48. Again, this technique requires grommeted sheet material and supporting assemblies that are relatively expensive.
A simpler known technique is to simply nail the edges of the sheet material to the mine surface or between the upper edge of a roof plate and the mine ceiling. However, this technique produces holes in the material that shortens its useful life. This technique also requires the use of hammer and nails, which complicate the installation process and add the risk of injury to the installer and damage to mining vehicle tires, and the nails do not reliably hold the curtain in place.
Several extensible line curtain structures have been proposed to permit line curtains to be readily extended toward the mine face. Examples include: U.S. Pat. No. 3,715,969 to Burgess; U.S. Pat. Nos. 4,180,352 and 4,282,802 to Divers, et al.; U.S. Pat. No. 4,440,070 to Baker, et al.; and U.S. Pat. No. 4,770,086 to Gabster. All of these structure are complex and expensive.